Gas decompression coolers, such as Joule-Thomson coolers, utilize the fact that a gas undergoing adiabatic expansion will be cooled. In such coolers, compressed gas is continuously fed into a tube which has a small aperture in it. The gas which escapes through the small aperture cools through its rapid expansion and exchanges heat with the incoming gas, thus partially cooling the incoming gas.
Joule-Thomson coolers are described in detail in the book Miniature Refrigerators for Cryogenic Sensors and Cold Electronics, written by Graham Walker and published by Oxford University Press, New York, 1989.
Due to the low temperature achieved at the aperture, impurities found in the gas accrete in the form of liquid drops or solids deposited over the interior of the tube near the aperture and/or within the aperture itself. This can cause partial or complete stoppage of the flow of the gas.
Under prevailing practices, in cases of light contamination, the operation of the cooler must be stopped, the cooler must be allowed to warm up, which takes approximately one-half hour, and then the cooler must be flushed with pure gas.
In cases of extreme contamination, the tube must be dismantled prior to its flushing with a cleaning liquid. The cleaning process is cumbersome and lengthy, typically taking a few hours.
As well-known in the art, some prior coolers are also utilized as gas purity testers, testing the purity of the gas by the amount of contaminants accumulated during a "test". At the start of each test, the cooler must be at a starting temperature which is typically considerably higher than the operating temperature to which the cooler is brought during a test. Thus, at the end of any test, a prior art cooler must be returned to its starting temperature, a process which typically takes again about 30 minutes.
It is an object of the present invention to provide a system capable to be used as a cooler which comprises improved means of expelling contaminants which accumulate inside a heat exchange tube and the aperture of the gas decompression cooler, such as a Joule-Thomson cryogenic cooler and/or a gas purity tester.
It is a further object of the present invention to provide an improved cooler comprising a cleaning system which does not require dismantling of the heat exchange tube and whose cleaning and warm-up periods are much shorter than those of the prior art.